1. Field of the Invention
This invention relates to rotary mowers for agricultural use and more particularly to rotary mowers of the type having at least two rotatable cutter units mounted side-by-side and each supporting at least one cutter blade to cut standing crop by impact, as opposed to shearing, during forward movement of the mower. The invention is particularly useful when applied to a combined rotary mower and crop conditioner, hereinafter referred to as a "mower conditioner,". The terms "forward" and "rearward" used throughout the specification are with respect to the direction of movement of the machine in operation.
2. Description of the Prior Art
Some rotary mowers currently in use have a cutter bar comprising a housing which accomodates the drive means for the rotary cutter units. In the operative position, the cutter bar housing extends substantially parallel to the ground and in a transverse direction relative to the forward operative movement of the mower. The rotatable cutter units are arranged substantially coplanar on top of the housing and in a side-by-side relationship, whereby the cutter units are driven from below. Each cutter unit normally comprises a shaped structure supporting at its outer periphery at least one cutter blade. The trajectories of the cutter blades of adjacent cutter units normally overlap each other at a location substantially in front of the drive housing in order to ensure a clean cutting action over the whole width of the cutter bar. The cutter blades operate as impact cutters and in order to provide a sufficient cutting impact, the rotational speed of the cutter units is relatively high. After being cut, the crop usually falls on top of the cutter units, the rotational movement of which ensures the discharge of the mown crop in a rearward direction relative to the cutter bar. However, if the forward speed of the mower is sufficiently high and the crop being cut is relatively tall and dense or tangled, the cutter units then tend to slide under the cut crop so as to leave it substantially in the same generally upright position as it was in prior to being out.
Although the capacity of rotary mowers is considerably greater than conventional reciprocatory sickle bar mowers, known rotary mowers still suffer many disadvantages. For example, in the underdriven type of mower discussed above, the drive housing forms the lowermost portion of the cutterbar, and is held close to the ground to maximise the quantity of mown crop. Since the crop to be mown is usually a green crop having a high moisture content and since the crop is often wet from rain or dew, there is a tendency for pieces of mown crop and/or dirt (soil, mud, etc.) to build up at the forward edge of the drive housing and to adhere thereto, particularly at the point where the trajectories of the cutter blades of two neighbouring cutter units overlap each other. This build-up also occurs at the location where the cutter blades move towards each other or at the locations where the cutter blades move away from each other. When these accumulations of crop and/or dirt are sufficient to extend beyond the points of intersection of the cutter blade trajectories, the standing crop can no longer come within the reach of the cutter blades because the accumulations deflect the standing crop in forward direction, whereby the cutter blades pass thereover. As a result, so-called "stripping" occurs which means that one or more strips of uncut crop are left which is a waste of valuable crop and which often causes problems during the subsequent hay making operations with hay tools such as tedders, rakes and balers.
This problem of stripping is aggravated by the fact that the cutter bar often strikes mole hills, etc., the resulting spread of soil tending to increase the rsik of dirt build-up on the forward edge of the cutter bar and also tending to pollute the mown crop.
Due to the high rotational speed of the cutter units, the cutter blades often hit the stems of the crop several times before the crop is discharged rearwardly of the cutter bar. Accordingly, a considerable portion of the crop becomes chopped into small pieces and apart from the increased risk of accumulation of this material on the cutter bar drive housing, this also constitutes another disadvantage in that the volume of useful crop is reduced. The risk of crop becoming chopped is especially great when difficult crop conditions are met such as, for example, a heavy crop, an extremely wet crop, a flattened crop, or an entangled crop.
Considerable power is consumed by this undesirable chopping action. Also the rotation of the cutter units creates considerable air turbulencies which tend to deflect the crop in a forward direction which prevents the mower from cutting the crops in a clean and even manner.
When the crop is flattened or entangled, for example as a result of bad weather conditions, a clean and even cut is often very difficult, if not impossible, to attain, as the cutter blades do not cut low enough with respect to the ground. This results in the crop being mown in inappropriate lengths, if it is cut at all.
Another diadvantage resides in the fact that, as the drive means extend below the cutter units and as the cutter units should be able to cut sufficiently low in order to avoid excessive stubble length, the cutter bar housing and the drive means have to be made very compact. This induces the manufacturer to make certain design compromises, which may be detrimental to quality. As it became practically impossible to cut sufficiently low with cutter units which have their axis extending vertically, the cutter units have been tilted to some extent in a forward direction. As a result thereof, the stubble length is no longer constant over the total width of the mower as so-called "scalloping" occurs which produces an unclean cut.
In another arrangement of known rotary mower, the rotatable cutter units are formed by cylindrical bodies mounted underneath a transversely extending main beam and having circular annular flanges at their lower ends for pivotally supporting the cutter blades. These cutter units are driven from the top instead of from beneath and, therefore, the drive means may be arranged inside the main beam. At the lower end, ground-engaging supports are normally arranged underneath each of the cutter units for supporting the structure on the ground. These ground-engaging supports may be stationary units or may be freely rotatable. Crop-engaging and discharging ribs may be mounted at the upper side of the flanges and at the outer circumference of the cylindrical body portion. Many of the disadvantages of the underdriven rotary mower have been eliminated, or at least attenuated, by the foregoing top driven or so-called "drum" mower. Indeed, a better conveying and discharging of the crops is obtained particularly by the provision of the cylindrical body portions and the provision of the crop-engaging and discharging ribs. The danger of the chopping of the crops and other disadvantages resulting therefrom have been avoided, or at least attenuated. Furthermore, a better control on the stubble height becomes possible as it is no longer necessary to provide drive means underneath the cutter blades. Also the cutter units can be held in an upright position, whereby scalloping is avoided. Nevertheless, it is possible to cut under practically all conditions, even under those conditions wherein the crop is completely flattened as the arrangement of components enables a sufficiently low cut to be effected.
Another major advantage of the drum mowers resides in the fact that, when the ground-engaging supports are freely rotatable, no build-up of dirt, etc., is likely to occur and consequently, all disadvantages resulting from such build-up are avoided.
Nevertheless, drum mowers do suffer from some substantial disadvantages. One disadvantage resides in the cantilever mounting of the cutter units on the main beam. During operation it may happen that a stone or other hard object of substantial dimensions gets jammed inbetween the flanges or drums of two neighbouring and oppositely rotating cutter units. This almost always results in considerable damage, for example the cutter units may be bent outwardly and away from each other, whereby substantial unbalance in the fast rotating components necessitates interruption of the operation of the machine to effect repair before the imbalance itself causes further damage. Also, the main beam and the drive means provided therein may become bent.
Another disadvantage resides in the fast does of bearing means for the freely-rotatable ground-engaging support discs which results from the considerable and uneven load of the latter. Indeed all the weight of the whole structure, which is supported on the ground, is transmitted to the ground via these discs and the bearings thereof. The considerable and uneven bearing load arises out of the weight of the structure and the fact that the discs normally contact the ground at a location which does not coincide with the axis of rotation thereof, so that with normal ground irregularities and a relatively high forward speed during operation of this type of machine, it will be appreciated that the bearing means for the support discs are indeed heavily and unevenly loaded causing fast wear thereof.
On the other hand, if the supporting elements underneath the cutter units of drum mowers were stationary elements, then these elements would dig into the ground and all the disadvantages of the build-up of dirt, etc. on such stationary elements which are inherent in the bottom or underdriven rotary mowers, would apply.
Mower conditioners having rotary type mower means are in use and each has a cutter bar which is principally similar to the underdriven or top driven rotary mowers discussed above. As a result, all disadvantages which are characteristic of such rotary mowers also apply to these mower conditioners. In addition, mower conditioners have other disadvantages.
All mower conditioners with a top driven rotary mower presently in use have a relatively complicated structure. The framework of the mower unit of such mower conditioners extends on top of the machine, whereas the conditioner means should extend in a transverse direction rearwardly of the mower units and at a comparatively small distance above the ground. Complicated modifications have therefore been made to the framework to arrive at a combined machine for both mowing and conditioning. In one mower conditioner, the conditioner means extend at a substantial distance behind the cutter units, whereby in operation, the crop which is cut by the mower units is first discharged onto the ground before being picked-up and conveyed to the conditioning means. This is clearly a disadvantage as the movement of the crop through the machine is not fluent, which may sometimes result in jamming and/or inadequate conditioning. Also the risk of stones and other hard objects entering the conditioning means and damaging the same is increased. Furthermore, the risk of chopping of the cut crop at the discharge end of the mower means may be substantial.
Other mower conditioners with top driven rotary mower means comprise additional transition components between the mower means and the conditioner means. These transition components are stationary and may obstruct the fluent and uniform transitional movement of the cut crop from the mower means to the conditioner means.
Another disadvantage of known mower conditioners resides in the fact that the structure is one complete unit wherein the mower means normally cannot easily be separated from the conditioner means so that the mower means cannot be used as an independent mower, and the conditioner means of one type cannot be interchanged with conditioner means of another type.
A further disadvantage resides in the fact that all known mower conditioner means are relatively heavy structures, which therefore are often in the form of pull-type machines rather than tractor-mounted machines. As a result, the manoeuvrability of the known pull-type mower conditioners is rather disappointing. Also as these machines are heavy and rather conplicated, they are relatively expensive to manufacture.